"Paul P" wrote in
message news:PerCh.3042$vu2.1488@trnddc04...
Does anyone have a guess what value choke L112 found here
http://www.ppinyot.com/hammarlund.ht...Supply%20Choke
might be? I am getting a 190 ac volt drop across this
puppy. It has a cold
DC resistance of 97 ohms. How I got there is also
explained at the
hyperlink page above.

The short of it is, the negative bias voltages are down
across all
associated tubes that share that supply. Google is no
help.

Even a guess at this point would be nice. I have never
calculated a choke in this configuration before.
Paul P

Just some thinking out loud (or maybe its finger
thinking).
1, Problems with chokes are usually either open windings,
shorted windings, or shorts to the case or core. Open
windings result in very high resistance or a completely open
circuit. Shorted windings result in lower than normal DC
resistance and lower than normal inductance. Shorts to the
case or core can be checked with an ohm meter. One can also
get high resistance "shorts" resulting in leakage from
winding to core. This is best tested using a special very
high resistance ohm meter. In any case, it does not sound
like you are having any of these problems.
The HX-50 appears to have three supplies, a high voltage
supply using the 5R4 rectifier with plates connected to the
outer windings of the xfmr, a low voltage supply using the
silicon diodes connected to the inner windings, and a
negative or bias supply using a single silicon diode
(CR-106) connected to the tap on the winding. If your bias
voltages are down but the B+ voltages are about normal I
would suspect the bias supply. Its possible the diode is bad
but they usually go either all the way open or all the way
shorted. A multimeter will check it. I am more suspicious of
the filter capacitors, C-176, C-177. Its also possible that
something has happened to R-168, the current limiting
resistor, or, perhaps one of the other resistors.
I wonder if anyone has a cross-reference between
Hammarlund part numbers and their specifications. I ran
across a web site that has a cross-reference between "old"
and "new" H part numbers, perhaps there is somesort of
catalogue there. I haven't looked. It would be useful to
know the inductance of L-112 and its DC resistance. The
inductance being off would also be an indicator of problem.
Again, if its the bias supply that has the problem I think
the choke is a red herring.


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Richard Knoppow
Los Angeles, CA, USA




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